1. Field of the Invention
This invention relates to a toner used in recording processes such as electrophotography, electrostatic recording, magnetic recording and toner jet recording.
2. Related Background Art
A number of methods as disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publication Nos. S42-23910 and S43-24748 and so forth are conventionally known as methods for electrophotography. In general, copies are obtained by forming an electric latent image (electrostatic latent image) on a photosensitive member by various means utilizing a photoconductive material, subsequently developing the latent image by the use of a toner to form a toner image, and transferring the toner image to a transfer medium (recording medium) such as paper as occasion calls, followed by fixing by the action of heat, pressure, heat-and-pressure, or solvent vapor. The toner that has not transferred and has remained on the photosensitive member is cleaned by various means, and then the above process is repeated.
In recent years, as a reflection of changing commercial needs for making composite, personal and so forth, such copying machines are severely sought to be made more small-sized, more light-weight, more high-speed and more highly reliable. As the result, performances required for toners have also become high-level.
In particular, one-component development making use of magnetic toners is preferably used because of its developing assembly having a simple structure, which may cause less troubles, has a long lifetime and may require only easy maintenance service.
Still in recent years, image-forming apparatus employing an electrophotographic technique, such as copying machines and laser beam printers, have been made to have various functions, and toner images to be formed are sought to be of high precision and high image quality. Accordingly, used are toners suited therefor and process cartridges making use of such toners.
For example, Japanese Patent Publication No. S51-23354 discloses a toner comprising a vinyl polymer cross-linked to an appropriate degree by adding a cross-linking agent and a molecular weight modifier. Also proposed are toners of a blend type comprising a vinyl polymer in which its glass transition temperature (Tg), molecular weight and gel content are specified in combination.
Such toners containing a cross-linked vinyl polymer or a gel content have an excellent effect on anti-offset properties. However, where such a cross-linked vinyl polymer is used in order to incorporate it in a toner, the polymer may have a very great internal friction in the step of melt kneading when the toner is produced, and a large shear force is applied to the polymer. Hence, in many cases, the cutting of molecular chains occurs to cause a decrease in melt viscosity, and this may adversely affect the anti-offset properties.
Accordingly, to solve this problem, it is proposed, as disclosed in, e.g., Japanese Patent Application Laid-Open Nos. S55-90509, S57-178249, S57-178250 and S60-4946, that, a resin having a carboxylic acid and a metal compound are used as toner materials and are heated and reacted at the time of melt-kneading to form a cross-linked polymer, which is then incorporated into the toner.
Japanese Patent Application Laid-Open Nos. S61-110155 and S61-110156 also disclose that a binder resin having as essential constituent units a vinyl monomer and also a special monoester compound is allowed to react with a polyvalent metal compound to carry out cross-linking through the metal.
Japanese Patent Application Laid-Open Nos. S63-214760, S63-217362, S63-217363 and S63-217364 still also disclose that a binder resin has a molecular weight distribution separated into two groups, a low-molecular weight resin component and a high-molecular weight resin component, and carboxylic acid groups incorporated into the low-molecular weight resin component are allowed to react with polyvalent metal ions to carry out cross-linking (a dispersion of a metal compound is added to a solution obtained by solution polymerization, followed by heating to carry out the reaction).
Japanese Patent Application Laid-Open Nos. H2-168264, H2-235069, H5-173363, H5-173366 and H5-241371 still also disclose toner binder compositions and toners in which the molecular weights, mixing ratios, acid values and their percentages of a low-molecular weight resin component and a high-molecular weight resin component in a binder resin are controlled to improve fixing performance and anti-offset properties.
Japanese Patent Application Laid-Open No. S62-9256 still also discloses a toner binder resin composition comprising a blend of two kinds of vinyl resins having different molecular weights and resin acid values.
Japanese Patent Application Laid-Open Nos. H3-63661, H3-63662, H3-63663 and H3-118552 still also discloses that a carboxyl-group-containing vinyl copolymer and an epoxy-group-containing vinyl copolymer are allowed to react with a metal compound to carry out cross-linking.
Japanese Patent Application Laid-Open Nos. H7-225491 and H8-44107 still also disclose that a carboxyl-group-containing resin reacts with an epoxy resin to form a cross-linked structure.
Japanese Patent Application Laid-Open Nos. S62-194260, H6-11890, H6-222612, H7-20654, H9-185182, H9-244295, H9-319410, H10-87837 and H10-90943 still also disclose toner binder resin compositions and toners in which molecular weight distribution, gel content, acid value, epoxy value and so forth are controlled in a resin composition constituted of a carboxyl-group-containing resin, using a glycidyl-group-containing resin as a cross-linking agent, to improve fixing performance and anti-offset properties.
These proposals disclosed as shown above, though having merits and demerits, have in fact attained good effects in respect of the improvement in anti-offset properties. There, however, are problems on developing stability and running performance when applied to magnetic toners for one-component development. Thus, a further improvement is required.